Reproducing digital signals

Abstract: To optically reproduce digital speech data recorded on an emulsifier surface (3) of a motion picture film (1), the film is illuminated with light (6) from the side of a base surface (2) of the film, and the light transmitted through the emulsifier surface (3) is collected as incident light by a reproducing lens (4). In this way, it is possible to reduce variations in the volume of light of the reproduced digital data which would otherwise be caused by scratches or dust present on the base surface (2) of the film (1).

Description: This invention relates to reproducing digital signals, for example digital speech data, optically recorded on a film, such as a motion picture film, or the like. If, in a transmission optical system, such as a microscope, the illumination efficiency is to be taken into account, it is desirable to equate the numerical aperture NA of the reproducing light with the numerical aperture of the illuminating light. In addition, for maximizing the resolution, it is preferred to set the numerical aperture of the illuminating light to 1.5 times that of the reproducing light. Consequently, in the conventional transmitting optical system, such as the microscope, the numerical aperture of the illuminating light is set so as to be not more than 1.5 times that of the reproducing light. The numerical aperture of the illuminating light is given by the sine of a divergence angle of a light ray with respect to the optical axis with a pinhole placed on an illuminated surface. It is now assumed that speech data is read from a conventional motion picture film 1 on which speech data has been recorded as a digital pattern, and signals are read from the side of a base surface 2 of the motion picture film, as shown in Fig. 1. In such case, should there exist a scratch 5 on the base surface 2, and should the numerical aperture of the illuminating light be larger than the numerical aperture of the reproducing lens 4, the scratch tends to be defocused to a lesser extent, so that the light of the image of the scratch 8 on the base surface 2 is collected by the reproducing lens 4. Consequently, when the light beam collected by the reproducing lens 4 is converted into electrical signals (digital signals), the resulting signals are corrupted significantly by the scratch 5. On the other hand, if the numerical aperture of the illuminating system is set to not more than 1.5 times of the numerical aperture of the reproducing system, the illuminating optical system of a complex structure is required, because a light guide having a larger divergence angle cannot be employed. In addition, if the digital speech data recorded on the motion picture film 1 is to be reproduced, with the numerical aperture of the illuminating system being set so as to be not more than 1.5 times as large as that of the reproducing system, the scratch or dust is raised in modulation factor, so that the reproduced digital signals are affected in an increasing amount. Furthermore, if the speech data on the motion picture film 1 is to be reproduced with a higher illumination efficiency and a high S/N ratio, it is necessary to employ a reproducing lens 4 having a higher value of the numerical aperture of the reproducing light. However, in such case, the depth of focus of the reproducing lens 4 becomes shallow, such that, when the speech data on the motion picture film 1 is reproduced, the reproduced digital signals are subjected to defocusing. Conversely, when the reproducing lens 4 of an extremely deep depth of focus is employed, focusing occurs not only an emulsifier surface 3, having the pattern of the speech data on the motion picture film 1 recorded thereon, but also the base surface 2, so that the light transmitted through the scratch on the base surface 2 or the dust is also collected, and hence the reproduced digital signal is affected significantly by the scratch or dust. PATENT ABSTRACTS OF JAPAN, vol 14, no. 577 (P-1146), 24 May 1985, which is an English language abstract of Japanese Patent Application Publication No. JP-A-60 006 939 (Shiyouichi Hasegawa) published 14 January 1985, discloses apparatus for reproducing a sound signal recorded on a film, in which the film is transported, a base surface of the film is irradiated with light, and an image of the recorded sound signal is enlarged and projected on to a slit via a lens. After passing through the slit, the light is incident on a photodetector. The film is irradiated with the light in any direction to eliminate the influence of a flaw or stain on the base surface, and uniform luminous flux is incident on the recorded sound signal to reduce noise. European Patent Application Publication No. EP-A-0 560 383 discloses an image scanner for a film in which the film is illuminated from one surface by reading light produced by illuminating means comprising a light source, an auxiliary condenser lens, slit members and further condenser lenses. After passing through the film the light is incident on a CCD line sensor via a reading (condenser) lens. The numerical aperture of each of the further condenser lenses of the illuminating means is set to be larger than the numerical aperture of the reading (condenser) lens. According to the present invention, there is provided apparatus for reproducing a digital signal optically recorded on a motion picture film having one surface forming a base surface and the other surface being an emulsifier surface carrying the recorded digital information, the apparatus comprising means for transporting the film; illuminating means for causing a beam of light to be incident on said base surface of the film; an objective lens facing the emulsifier surface for condensing the light after transmission through the film; and means for producing an electrical signal of a signal level related to the intensity of the light condensed by the objective lens; wherein the numerical aperture of the light beam from the illuminating means incident on the film is set to be not less than 1.5 times the numerical aperture of the objective lens, and wherein the depth of focus, d, of the objective lens fulfils the relationship z ≤ d ≤ t where z is the film wobbling defined as the variation in the position of the film along the focusing direction and t is the thickness of the film. When the digital signal optically recorded on the film is reproduced with transmitted light, the film is arranged with its base surface facing the illuminating means or system and with its emulsifier surface facing the objective lens, whereby the illuminating light is radiated from the side of the base surface for illuminating the digital signal (e.g. a digital speech data pattern) recorded on the emulsifier surface. Consequently, it becomes possible to reduce the variation in the volume of the light of the reproduced digital signal otherwise produced by a scratch or dust possibly present on the film base surface. Since the numerical aperture of the illuminating light radiated from the film base surface is set so as to be 1.5 times or more as large as the numerical aperture of the objective lens, it becomes possible to diminish adverse effects of scratches or dust on the reproduced digital signals. In addition, simplified illumination may be realized with the use of a light guide having a larger outgoing angle. Furthermore, if, as is preferred, the numerical aperture of the objective lens facing the emulsifier surface of the film is set to be not less than 0.06 and not more than 0.16, the depth of focus of the objective lens can be set so as to be larger than the film surface variation along the focusing direction, so that, when reproducing the digital signal optically recorded on the film using the transmitted light, it becomes possible to provide for a margin for defocusing of the image of a scratch or dust possibly present on the film base surface and hence to decrease the adverse effects of the scratches or dust on the reproduced digital signals. Embodiments of the invention described hereinbelow provide an apparatus for reproducing a digital signal optically recorded on the base surface of a film in which it is possible to reduce adverse effects caused by scratches or dust possibly present on the film base surface. The invention will now be further described, by way of illustrative and non-limiting example, with reference to the accompanying drawings, in which: Fig. 1 shows a schematic arrangement of an apparatus employing a previously proposed digital signal reproducing method; Fig. 2 shows a schematic arrangement for illustrating the principle of digital signal reproducing apparatus embodying the invention; Fig. 3 shows a schematic arrangement of an apparatus according to an embodiment of the invention for reproducing a digital signal; Fig. 4 shows a schematic arrangement of an apparatus according to a second embodiment of the invention for reproducing a digital signal; Fig. 5 shows a schematic arrangement of an apparatus according to a third embodiment of the invention for reproducing a digital signal; and Fig. 6 shows a schematic arrangement of a light source side of apparatus embodying the invention for reproducing a digital signal. Referring to the drawings, preferred embodiments of the present invention will be explained in detail. Fig.2 shows a schematic arrangement for illustrating the principle of digital signal reproducing apparatus embodying the present invention. In Fig.2, a pattern of digitally recorded speech data on an emulsifier surface 3 of a motion picture film 1 is illuminated by an illuminating light beam 6 from a base surface 2 of the motion picture film 1. The light beam transmitted through the emulsifier surface 3 is collected as an incident light beam 7 by a reproducing lens 4. At this time, a scratch 5 present on the base surface 2 is also illuminated by the illuminating light beam 6, so that an image 8 of the scratch 5 is formed on the emulsifier surface 3. However, since the image 8 of the scratch 5 reaching the emulsifier surface 3 is defocused so that the volume of light of the image 8 of the scratch 5 collected by the reproducing lens 4 is small. Thus the reproduced speech data is affected to a lesser extent by the scratch or dust. Fig.3 shows a schematic arrangement of an apparatus for carrying out the above-described digital signal reproducing method. An illuminating light beam from a halogen lamp 11 is incident on a light guide 13 via a mirror 12 and is conducted by the light guide 13 as far as a motion picture film 14 wrapped around a drum 15. The motion picture film 14 is arranged so that the base surface 2 and the emulsifier surface 3 are directed to the halogen lamp 11 radiating the illuminating light beam and to an objective lens 16, respectively. The light guide 13 has its outgoing end 13R shaped to a rectangle for mating with an illuminated region. The illuminating light beam transmitted through the motion picture film 14 is collected by the objective lens 16 and thence routed to a CCD 17 which then outputs electrical signals of a signal level related to the received light volume. In the present embodiment, the pattern of the speech data digitally recorded on the motion picture film 14 is imaged on the CCD 17 with a multiplication factor of four by the objective lens 16. The objective lens 16 has its depth of focus d ( = λ/NA 2 ) related with the thickness t of the motion film 14 and a variation (film wobbling) along the focusing direction of the motion picture film 4 by the following formula (1): z ≤ d ≤ t where λ denotes the wavelength of the illuminating light and NA the numerical aperture of the objective lens 16. Meanwhile, the film variation is produced by various factors, such as mechanical tolerances of the drum, setting errors in bearings retaining the drum, film deformation produced by the film not being cut correctly to 35 mm width or film deformation produced on punching film perforations, etc. By measurement, the thickness t of the motion picture film 14 is 160 µm, while the variation z along the focusing direction of the motion picture film 14 is 20 to 30 µm. Thus the following formula 20 ≤ d ≤ 160 is found from the above formula (1). The wavelength λ of the illuminating light outgoing from the halogen lamp 11 is 530 nm, so that the following formula (3) 20 ≤ 0.53/NA 2 ≤ 160 is derived. Ultimately, the numerical aperture NA of the objective lens 16 assumes a value shown by the following formula (4): 0.06 ≤ NA ≤ 0.16 Thus, by setting the numerical aperture NA of the objective lens 16 to, for example, 0.1, there is no longer a risk of the speech data reproduced from the motion picture film 14 being defocused and thereby deteriorated by variations in the motion picture film 14. On the other hand, since the image of the scratch or dust on the base surface 2 of the motion picture film 14 is defocused before reaching the objective lens 16, such scratch or dust operates less detrimentally on the reproduced digital speech data. Meanwhile, it is disclosed in "OYO KAGAKU" (Applied Chemistry) I, by Tatsuro Asakura, published by ASAKURA SHOTEN, that the maximum resolution is achieved when the NA of the illuminating system is set to approximately 1.5 times that of the objective lens. However, in such case, the resolution of the scratch or the dust is also undesirably elevated. However, if the numerical aperture of the illuminating system is elevated, the transmitted light through the scratch or the dust, conducted out of the aperture of the objective lens 16, comes within the field of view of the objective lens 16, thus rendering it possible to lower the modulation factor of the scratch or the dust. Consequently, by setting the numerical aperture of the illuminating system so as to be not lower than 1.5 times that of the objective lens 16, the scratch or the dust operates less detrimentally on the reproduced speech data. If the motion picture film 14 is arranged with its emulsifier surface directed towards the light guide 13 for illuminating the pattern of the speech data recorded on the emulsifier surface, the light transmitted through the speech data pattern is read out after being transmitted through the scratch or dust on the base surface. If the speech data pattern is illuminated from the base surface of the motion picture film 14, the illuminating light from the light guide 13 transmitted through the scratch or the dust before reaching the emulsifier surface having the speech data pattern recorded thereon. If the adverse effect of the scratch or the dust is to be reduced, it is necessary to raise the numerical aperture of the objective lens 16 for reducing the depth of focus in order to defocuses the image of the scratch or the dust which lies ahead. However, in the latter case, it is possible to elevate the numerical aperture of the illuminating light in order to defocus the image of the scratch or the dust on the emulsifier surface. On the other hand, since the numerical aperture of the illuminating system can be set so as to be larger than the numerical aperture of the objective lens 16 which is limited by the variations in the motion picture surface, the adverse effect of the scratch or the dust may be decreased by causing the illuminating light to fall from the base surface of the motion picture film 14. If the numerical aperture of the illuminating system is set so as to be not less than 1.5 times as large as that of the objective lens 16, it is more preferred to arrange the emulsifier surface of the motion picture film 14 on the side of the objective lens 14 instead of on the side of the light guide 13. This diminishes the effects of the scratch or the dust present on the base surface of the motion picture film 14. In the above embodiment, description has been made of reading speech data digitally recorded on the motion picture film 14 using the illumination from the light guide 13. Alternatively, the speech data recorded on the motion picture film 14 may be read out using the critical illumination or Koehler illumination. Figs.4 and 5 show typical practical arrangements of the illuminating system for these cases. The signal readout side employing the transmitted light from the motion picture film 14 as the readout light is configured similarly to the arrangement shown in Fig.3. The numerical aperture of the illuminating system denotes the condenser lens aperture ratio. Fig.4 shows a second practical arrangement of the digital signal reproducing apparatus employing the critical illumination. In the present arrangement, the illuminating light outgoing from a light source made up of a halogen lamp 11 and a mirror 12 is collected by a condenser lens 10 via a field stop 18 having a rectangular aperture matched to an illuminated region and an aperture stop 19 governing the numerical aperture of the illuminating system, and is caused to fall on the motion picture film 14 wrapped around the drum 15. The motion picture film 14 is arranged so that its base surface is illuminated by the illuminating light from the halogen lamp 11 and its emulsifier surface faces the objective lens 16. Fig.5 shows a third practical arrangement of the digital signal reproducing apparatus employing the critical illumination. In the present arrangement, the illuminating light outgoing from a light source made up of a halogen lamp 11 and a mirror 12 is collected by a lens 9 via a field stop 18 having a rectangular aperture matched to an illuminated region on an aperture stop 19 governing the numerical aperture of the illuminating system. The outgoing light from the aperture stop 19 is caused to fall via the condenser lens 10 on the motion picture film 14 wrapped around the drum 15. The motion picture film 14 is arranged so that its base surface is illuminated by the illuminating light from the halogen lamp 11 and its emulsifier surface faces the objective lens 16. In the above-described three embodiments, the halogen lamp is employed as the right source. In place of the halogen lamp, light sources of a smaller size, such as LEDs or LDs, may also be employed. Specifically, such an illuminating device may be employed in which the outgoing light from the LED 21 is converted by a light-scattering plate 22 into a uniform illuminating light illuminating the motion picture film 14.

Claims: Apparatus for reproducing a digital signal optically recorded on a motion picture film (1; 14) having one surface (9) forming a base surface and the other surface (3) being an emulsifier surface carrying the recorded digital information, the apparatus comprising means for transporting the film (14); illuminating means for causing a beam of light to be incident on said base surface (2) of the film; an objective lens (16) facing the emulsifier surface (3) for condensing the light after transmission through the film; and means (17) for producing an electrical signal of a signal level related to the intensity of the light condensed by the objective lens; wherein the numerical aperture of the light beam from the illuminating means incident on the film is set to be not less than 1.5 times the numerical aperture of the objective lens, and wherein the depth of focus, d, of the objective lens (16) fulfils the relationship z ≤ d ≤ t where z is the film wobbling defined as the variation in the position of the film along the focusing direction and t is the thickness of the film. Apparatus as claimed in claim 1, wherein the numerical aperture of the objective lens (16) is set to be not less than 0.06 and not more than 0.16. Apparatus as claimed in claim 1 or claim 2, wherein the illuminating means comprises a light source (11, 12) and a light guide (13) for radiating the light beam from the light source at a pre-set position on the film. Apparatus as claimed in claim 1 or claim 2, wherein the illuminating means comprises a light source (11, 12), a field stop (18) for adjusting the field of view of the light beam from the light source for matching to the illuminated region, an aperture stop (19) for setting the numerical aperture of the light beam radiated on the film to a pre-set value, and a lens (10) for collecting the light beam via the aperture stop (19) for radiating the light beam at a pre-set position on the film. Apparatus as claimed in any one of the preceding claims, wherein said means (17) for producing an electrical signal is a CCD.

Inventors: NAKAO TAKASHI, NAKAO, TAKASHI, NAKAO, TAKASHI, C/O INTELLECTUAL PROPERTY DIVISION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1994
Main classification: G03B31
IPC codes: G11B7, G03B31